1. Field of the Invention
The present invention relates generally to analog integrated circuits. More specifically, a low voltage bipolar transconductor circuit with extended dynamic range is disclosed.
2. Description of Related Art
A transconductor circuit is a circuit that converts a voltage input into a current output. The output of a transconductor circuit is dependent upon its gain, measured in units of conductance. The gain of a transconductor circuit is determined by the ratio of its output current I.sub.O to the input voltage V.sub.IN. The ratio I.sub.O /V.sub.IN is defined as the transconductance and is generally represented by g.sub.m.
Typically, a transconductor circuit has two voltage inputs V.sub.1 and V.sub.2. In a normal mode of operation, the input voltages are changed differentially, independent of each other. In a common mode of operation, both input voltages change levels together. Transconductor circuits are often used as linear amplifiers. Measures of the performance of a transconductor circuit operating as a linear amplifier are its input voltage handling capability and its dynamic range.
U.S. Pat. No. 5,289,136, the entirety of which is incorporated by reference herein, discusses several examples of transconductance-based amplifiers such as emitter-coupled pair, series diode linearization, transistor ratio linearization, two differential pairs with ratios in parallel, and amplifiers using level shift techniques.
In analog signal processing, the typical frequency range of operation of linear circuits continues to increase with technological advances. Currently the typical frequency range of operation of linear circuits extends into several hundred Megahertz (MHz) and, in some cases, into the Gigahertz (GHz) range. The high frequency range of operation of linear circuits has been enabled by smaller geometries of integrated chips, necessitating in decreasing supply voltage operation.
For high speed considerations, the bipolar transistor is favored in linear circuits. However, the decrease in supply voltage is placing severe challenges in the design of such bipolar transistor linear circuits.
Accordingly, what is needed is a low supply voltage bipolar transconductor circuit having extended dynamic range which overcomes the supply voltage overhead problem. Preferably, the bipolar transconductor circuit can be operated at a low supply voltage and provide extended dynamic range without sacrificing signal handling capability and performance. Such a low supply voltage bipolar transconductor circuit having extended dynamic range would be particularly useful in high performance, high frequency analog circuits. Examples of such high performance, high frequency analog circuits include differential amplifiers, comparators, and filter transconductor elements.